Stretching, exercising injured knee, neck

One of my friends tweaked her knee recently while working out. I told her I would do some research on appropriate exercises/stretches for an injured knee.
Even when you are careful while exercising you can still hurt yourself. The other day in an opening over the bolster yoga pose I was careful and slowly turned my neck and still somehow pulled a muscle in my neck.
I did some neck stretches, like some of the ones mentioned in this Livestrong article, and I also used a neck pillow my mother-in-law made me, which is filled with rice and lavender. The pillow can be heated up in the microwave or put in the freezer.
The warmth of the pillow helped my neck while also comforting me and keeping me warm.
My neck is feeling a lot better. But I am trying to be careful with it.
But back to the real reason for this post: My friend’s hurt knee.
According to another Livestrong article, to help with an injured knee one needs to be strengthening and stretching two important leg muscles–the quadriceps and hamstring.
According to this article, knees are the most commonly injured joints in the body. The linked article gives you 11 exercises to help decrease knee pain.
There are so many great articles online, which give lots of advice and possible exercises. I am going to link up to one more. If you think you need more information than I have provided feel free to research even more and hey, if you find something else the articles I linked up to don’t address, please let me know.